The invention relates to a rack for supporting wafers for treatment and, in particular, semiconductor substrate wafers for a gas and heat diffusion surface treatment.
Racks for supporting circular semiconductor substrate wafers for treatments are known from German design patent publication No. 80 21 868, for example. German patent publication No. 3,624,751 discloses another such supporting rack in the form of a trough-like supporting body with slot-like kerfs in its bottom and in the upper edges of its side walls in which individual semiconductor substrate wafers are inserted.
When loaded with semiconductor substrate wafers, such racks are put into horizontally-operated diffusion furnaces for heat and gas treatment of the surfaces of semiconductor substrate wafers. To facilitate handling for this, it has long been the practice to make the racks relatively short, typically with a length of 150 mm and a capacity for 25 or 50 wafers. The usual diffusion furnace holds from three to seven such racks at a time.
Also to facilitate handling in putting such racks into a furnace, the ends of the racks have had handles. The space required for the handles has resulted in more space between the rack-end substrate wafers in successive racks placed end to end in the furnace than between the substrate wafers in either of the racks. This has resulted in non-uniform gas and heat flow about the substrates in the furnace and, thus, non-uniform gas and heat treatment of the rack-end wafers in the furnaces as compared to wafers not at the ends of either of the end-to-end racks. The extra, handle-caused end spacing between end-to-end racks also was wasted, giving the racks an unfavorable useful-to-total length ratio.